Cristina-Maria Valcu, Richard Scheltema, Ralf Schweiggert, Mihai Valcu, Kim Teltscher, Dirk Walther, Reinhold Carle, Bart Kempenaers

Maternal investment directly shapes early developmental conditions and therefore has long-term fitness consequences for the offspring. In oviparous species prenatal maternal investment is fixed at the time of laying. To ensure the best survival chances for most of their
offspring, females must equip their eggs with the resources required to perform well under
various circumstances, yet the actual mechanisms remain unknown. Here we describe the
blue tit egg albumen and yolk proteomes and evaluate their potential to mediate maternal
effects. We show that variation in egg composition (proteins, lipids, carotenoids) primarily
depends on laying order and female age. Egg proteomic profiles are mainly driven by laying
order, and investment in the egg proteome is functionally biased among eggs. Our results
suggest that maternal effects on egg composition result from both passive and active (partly
compensatory) mechanisms, and that variation in egg composition creates diverse biochemical environments for embryonic development.